Purification and Structural Analysis of a Latent Form of Transforming Growth Factor-β from Rat Platelets

Abstract

A latent form of transforming growth factor type-β(TGF-β) with a high molecular weight was purified to homogeneity from rat platelets by a six-step procedure. The yield of the purified latent TGF-β from platelets of 2, 500 rats was 1.4mg. The purified latent TGF-β was activated by treatment with urea at concentrations of over 4M or acidic solutions of below pH4. SDS-PAGE and gel filtration chromatography showed that the latent TGF-β consisted of active TGF-β and glycoproteins of about 200kDa as masking components, and that under physiological conditions, these components formed a high molecular weight complex of about 400kDa linked by non-covalent bonds. Here, we found that the masking protein was composed of one large subunit of about 110kDa and two small subunits of 39kDa linked by disulfide bridges. The N-terminal amino acid sequence of the small subunit was identical to the N-terminal region of the TGF-β precursor lacking a signal peptide. From these findings, we proposed a structural model for the latent TGF-β from rat platelets.